The present invention relates to an apparatus and a method for determining an overlap length of wound-up materials, and particularly to how the overlaps, which may occur at the end of winding up a material strip on a carrier body, can be determined reliably and with high precision.
Apparatuses and/or methods in which the overlap length of materials wound and/or applied onto a carrier in layers is to be determined are required in many applications.
For example, when laminating glass fiber mats or carbon fiber mats, the mats are applied in layers, wherein the layers must not abut each other bluntly, but rather should have a specified overlap for achieving maximum stability. This means that the new mat following a mat already applied is to cover the applied mat by a predetermined length at its contact area.
Similar problems may also arise when winding up band- or strip-shaped material on a carrier or a drum or a base body. In some such cases of application, such as winding up a cable and/or a winding of a coil or the like, it may also be necessary to determine the overlap of the end of the wound cable with the underlying sheets, so as to obtain a coil with a particularly homogenous magnetic field, for example, in which the overlap of the last winding is approximately zero. This may be particularly relevant in coils with few individual windings.
A broad field of application, for example, also is the manufacturing process of car tires, wherein individual strip- or band-shaped rubber sheets are wound onto a base body, for example, or to the casing already put up. For example, the base body may be a drum of cylindrical geometry or another rotation-symmetrical body consisting of individual straight segments, the circumference of which has a circular and/or cylindrical envelope. What is to be achieved as a final product here is a tire having a thickness as constant as possible perpendicular to its circumference, the wall thickness of which is thus as uniform as possible so as to avoid height run-out in the finished product, for example. Typically, the most diverse materials are combined with each other here so that, in some manufacturing methods, band- and/or strip-shaped rubber strips of predetermined lengths are wound onto a rotating carrier, wherein the end of the strip-shaped wound material may overlap with the beginning of the same material strip. This overlap may be intended, but its overlap length, i.e. generally speaking that region in which the beginning and the end of the same material strip usually overlap, needs to satisfy exactly predefined geometric boundary conditions.
On the one hand, the length in the tangential direction, i.e. along the expansive dimension or winding direction of the material strip, may here be regarded as the overlap length. Alternatively, also the offset that may develop due to the fact that the material strip is not superimposed identically at the beginning and at the end transversely to its winding direction (in the width direction), i.e. in the axial direction parallel to the axis of the rotating body, may also be regarded as the overlap length.
Generally speaking, it is often required to determine geometrical properties of the wound material and/or the surface of the wound material. Among other things, negative overlap lengths, i.e. gaps in the surface developing when the wound material is too short, may also be of interest here. An offset of a wound material between the beginning and the end of the winding also often has to be controlled. Generally, it is often required to determine a distance measure between certain characteristic points of a wound-up material strip, as well as the distance measure between the beginning (starting edge) and the end (end edge) of the material strip, for example.
In other words, for example, various material sheets are wound successively onto a tire construction drum in the production of vehicle tires, for example. Here, faulty overlap lengths of the various materials may develop, which may significantly affect the mechanical properties, and hence the stability, of the tire. Detection of such faulty conditions, particularly of open splice (the gap or overlap between the beginning and the end), and correction and/or segregation of such wound material is hence desirable. An open splice is to be understood as the condition in which the material strip does not overlap at all with the beginning of the material strip at its end, so that an area not covered by wound material is obtained.
One difficulty in the measurement of the overlap length of overlapping materials is that only the material end edge is still visible on the outside after the winding operation, because the starting edge of the material itself is covered in the end and/or overlap area. This results in the fact that it is not possible to perform exact measurement of the overlap length merely due to the measurement of the overlap area itself.
Previously, for checking the overlap length during the industrial fabrication, for example human examiners, who performed a subjective assessment of the overlap length after the finished winding, were often employed. On the other hand, it has been attempted to employ measurement methods and/or sensors working point by point, which generate a binary output signal, i.e. in which the sensor itself immediately detects the presence of an edge.
For example, this may be achieved by way of optical sensors, which react to the brightness change caused by reflected light on a sensor. If a new sheet is applied and/or a sheet overlaps, the point at which irradiated light is reflected approaches the stationary sensor so that it detects an altogether increased radiation intensity. When a certain limit value is exceeded, the detector then indicates the presence of an edge. Apart from the fact that such a sensor works either point by point or that it is only possible to determine a few measurement points this way in materials having a certain width, these binarily working methods cannot be employed without extended control logic, among other things, in the control of a frequently occurring scenario, the measurement of the overlap length of so-called “blunt splices”, i.e. of wound materials with a target overlap length of 0. In the normal case of the desired seamless transition, such a sensor cannot detect an edge, so that the following evaluation logic obtains an invalid input signal.
Even if the logic could interpret such a missing input signal correctly, applications in which the wound material does not have any abrupt starting or end edge, e.g. because it is chamfered, could not be controlled satisfactorily with such sensors. In some applications, such an edge-detecting sensor is used to first detect the starting edge of the material strip to be wound up during a winding process, wherein the associated angular position of the drum is detected by means of an angular measurement means at the same time. After winding up the material and/or during winding up, the end edge of the material strip is detected after (approximately) a single drum revolution, and the associated angular position of the drum is detected at the same time. From the difference of the two absolute angular positions of the drum and the mandatorily previously known drum radius, the length of the material strip is determined, and then the resulting overlap length of the material is calculated if the drum circumference is known.
In some application scenarios partially already discussed briefly above, such a method and/or such an apparatus implementing such a method cannot lead to any positive result. If the material and/or the material beginning does not start abruptly with a perpendicular edge, for example, but is cut flat (i.e. starts with a cutting angle in the tangential direction of <45°, for example), unequivocal determination of a position value of the starting edge cannot be performed. Frequently used angular drums and/or base bodies, which are structured such that individual axially parallel segments alternate with interposed open gaps, per se have a multiplicity of successive edge structures, so that the application of the above-described method is not possible here. This is the case even in a continuous, i.e. for example round surface of the winding drum if material strips already wound previously have an overlap, and hence lead to an end edge.
In the “blunt splice” case of application and with obliquely cut material, recognition of the material end edge, and hence measurement of the material overlap, is thus not possible either, since the starting and end edges virtually join seamlessly in the error-free case, and hence there is no detectable edge. When cut obliquely, a slight overlap, which leads to only a minimal, but possibly already disturbing height difference, cannot be detected if the height difference lies below the threshold value limit of the edge-sensitive method.
Basically, in these conventional methods, the end edges often cannot be determined and/or unambiguously associated because of structures due to material overlap from the material preparation, from the underlying sheets, and because of other spurious effects, such as wrinkling, material structuring, drum structuring, etc. The detection of material properties in the axial direction is not possible either in these methods.
Hence, there is the need to provide an apparatus and/or a method allowing for more reliable measurement of wound-up materials strips with respect to geometrical features, such as distance measures.